The stm-io-hooks package

This library provides a Software Transactional Memory (STM) monad with commit and retry IO hooks.
A retry-action is run (at least once) if the transaction retries, while commit-actions are
executed iff the transaction commits. The AdvSTM monad also gives some atomicity
guarantees for commit-actions:

When a TVar is modified in a transaction and this transaction commits,
the update remains invisible to other threads until the corresponding
onCommit action is run.

If the onCommit action throws an exception, the original values of
the modified TVars are restored.

Note: The package can be used as a drop-in replacement for
Control.Concurrent.STM.